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Miniature pump for liquid cooling systemRelated Patent Categories: Pumps, Motor Driven, Electric Or Magnetic Motor, Rotary Motor And Rotary Nonexpansible Chamber Pump, Having BearingMiniature pump for liquid cooling system description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070224059, Miniature pump for liquid cooling system. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] The present invention relates generally to pumps, and more particularly to a miniature pump having a magnetically levitated impeller for a liquid cooling system for cooling an electronic package. DESCRIPTION OF RELATED ART [0002] With the continued development of computer technology, electronic packages such as the CPUs are generating more and more heat that needs to be dissipated immediately to avoid damage to the circuitry. Conventional heat dissipating devices such as heat sink/fan combinations are not sufficiently effective at dissipating heat to cope with modern circuitry. Liquid cooling systems have thus been increasingly used in computer technology to cool these electronic packages. [0003] A typical liquid cooling system comprises a heat absorbing unit for absorbing heat from a heat source, and a heat dissipating unit which is filled with liquid. The liquid exchanges heat with the heat absorbing unit, thereby taking away the heat of the heat absorbing unit as the liquid is circulated. Typically, a pump is used to circulate the liquid. [0004] Generally, the pump comprises a housing having a bottom plate, a shaft having a bearing pivotably attached thereto, an impeller received in the housing and attached to the bearing, a magnetic coupling structure, and a motor. The shaft passes through the impeller and engages with the bottom plate of the housing. The magnetic coupling structure comprises an inner magnet mounted on the impeller and an outer magnet appropriately disposed on the motor outside of the pump housing. In operation, the motor rotates to drive the outer magnet to rotate therewith. The inner magnet receives the attractive force of the outer magnet, so that the inner magnet is caused to rotate at a high speed as a result of the high-speed rotation of the outer magnet, thus causing the impeller to rotate with high-speed. The impeller thus rotates with the inner magnet to circulate the liquid in the liquid cooling system, thereby taking away the heat. However, a problem existing in the conventional pump is that during the high-speed rotation of the pump there is friction between a bottom of the bearing and the bottom plate of the housing of the pump because the axial attract force of the outer magnet is applied on the impeller having the inner magnet, which causes damage to the pump housing. A way of reducing the friction between the bearing and the pump housing is that a wearable washer is mounted between the bearing and the bottom plate of the pump housing, however this can result in high levels of unwanted noise pollution. [0005] Therefore, there is a need for a pump with a low-friction bearing SUMMARY OF INVENTION [0006] According to a preferred embodiment of the present invention, a miniature pump comprises a pump casing and a liquid circulating unit received in the pump casing. The pump casing comprises a hollow main body transversely forming a spacing plate and a partition wall separated from the spacing plate. The liquid circulating unit comprises a shaft mounted between the partition wall and the spacing plate, a bearing rotatably mounted mounted to the shaft, an impeller attached to the bearing to rotate therewith, a first pair of spaced magnetic spacers surrounding an upper portion of the shaft and positioned above the bearing, and a second pair of spaced magnetic spacers surrounding a lower portion of the shaft and positioned below the bearing. The two pairs of magnetic spacers suspend the impeller in a stable position in an axial direction of the pump when the impeller rotates so that the impeller is prevented from rubbing against the partition wall when the impeller rotates. [0007] Other advantages and novel features of the present invention will become more apparent from the following detailed description of preferred embodiment when taken in conjunction with the accompanying drawings, in which: BRIEF DESCRIPTION OF DRAWINGS [0008] FIG. 1 is an exploded, isometric view of a miniature pump according to a preferred embodiment of the present invention; [0009] FIG. 2 is an assembled view of the miniature pump of FIG. 1; and [0010] FIG. 3 is a cross sectional view taken along line III-III of FIG. 2. DETAILED DESCRIPTION [0011] Referring to FIGS. 1 and 2, a miniature pump in accordance with a preferred embodiment of the present invention comprises a pump casing 10 having an inner space, and a liquid circulating unit 20 and a motor driving unit 30 received in the inner space of the pump casing 10. [0012] The pump casing 10 comprises a hollow main body 14, a top cover 12 hermetically attached to a top end 140 of the main body 14, and a bottom cover 16 attached to a bottom end 143 of the main body 14. A sealing ring 141 is disposed between the main body 14 and the top cover 12 to prevent liquid leakage. The top cover 12 forms an annular groove 120 at a bottom edge thereof for receiving the sealing ring 141 therein. An inlet 122 is formed on the top cover 12 for allowing liquid to enter the pump casing 10. An outlet 142 is formed on the main body 14 for allowing the liquid to exit the pump casing 10. [0013] The main body 14 transversely forms an inner partition wall 144. This partition wall 144 effectively divides the inner space of the main body 144 into a top space 146 and a bottom space 148. [0014] Referring also to FIG. 3, a spacing plate 126 is transversely arranged in the main body 14 as a guide means. The spacing plate 126 further divides the top space 146 of the main body 14 into a first chamber 145 between the spacing plate 126 and the top cover 12, and a second chamber 147 between the partition wall 144 and the spacing plate 126. A round cap 1260 protrudes upwardly from a center of the spacing plate 126. A protrusion 1262 having an inner space communicating with the cap 1260 protrudes from a top of the cap 1260. A plurality of through openings 1264 is defined in the spacing plate 126 adjacent to the cap 1260 to intercommunicate the first and second chambers 145, 147. [0015] Referring to FIGS. 1 and 3, the liquid circulating unit 20 is mounted in the second chamber 147 of the pump casing 10. The liquid circulating unit 20 comprises a shaft 25 mounted between the partition wall 144 and the spacing plate 126, a bearing 27 pivotably attached to the shaft 25 and a magnetically levitated impeller 26 attached to the bearing 27. A first permanent magnet 261 is embedded in the impeller 26. The first permanent magnet 261 has a substantially ring-shaped flat body magnetized so as to have a plurality of alternating N and S poles along the ring body. The impeller 26 comprises a center hollow post 260 having a receiving room and a plurality of alternating first and second blades 262, 263, wherein the first blades 262 extend from the center post 260 to an outer edge portion of the impeller 26, and the second blades 263 are formed at the outer edge portion of the impeller 26. For positioning the shaft 25, the partition wall 144 forms a shaft support 1440 having a center blind hole 1442 receiving a bottom end of the shaft 25 therein, and a top end of the shaft 25 engages in the inner space of the protrusion 1262 of the spacing plate 126. An annular recess 1444 communicating with and surrounding the blind hole 1442 is defined in the shaft support 1440. [0016] The motor driving unit 30 is received in the bottom space 148 of the pump casing 10. The motor driving unit 30 is positioned on the bottom cover 16 and comprises a motor having a rotor 32. A second permanent magnet 320 is attached to the rotor 32 for rotating therewith, in a position corresponding to that of the first permanent magnet 261 with a flux gap formed therebetween. Like the first permanent magnet 261, the second permanent magnet 320 also has a ring flat body magnetized so as to have a plurality of alternating N and S poles along the ring body. [0017] In operation, the rotor 32 of the motor driving unit 30 rotates so as to drive the second permanent magnet 320 to rotate therewith. The first permanent magnet 261 is driven to rotate with second permanent magnet 340 by the attractive magnetic force therebetween. The impeller 26 thus rotates with the first permanent magnet 261 to circulate the liquid in the liquid cooling system. In the present invention, the impeller 26 uses four annular magnetic spacers 21-24 to control its axial position, wherein the magnetic spacers 22, 23 are received in two opposite ends of the impeller 26 and rotate with the impeller 26, the magnetic spacers 21, 24 are respectively fixedly received in the spacing plate 126 and the partition wall 144. The magnetic spacers 21, 22 surround an upper portion of the shaft 25 without connection therewith and are positioned above the bearing 27. The magnetic spacers 21, 22 are spaced and opposite to each other, wherein the magnetic spacer 21 is received in the cap 1260 of the spacing plate 126 and the magnetic spacer 22 is received in an upper portion of the receiving room of the post 260. Each of the magnets 21, 22 has a north (N) pole and an opposite south (S) pole. The magnetic spacers 21, 22 are arranged so that the S pole of the magnetic spacer 21 opposes the S pole of the magnetic spacer 22. The like magnetic poles oppose each other so that a repulsive force F1 exists between the magnetic spacers 21, 22, which means the impeller 26 with the magnetic spacer 22 is pushed downwards with force F1 by the magnetic spacer 21. When the impeller 26 rotates, the impeller 26 acts on the liquid with centrifugal force. Simultaneously, the liquid acts on the impeller 26 with a corresponding force F. The force F has an upward component F4 where the liquid acts on the impeller 26 in an axial direction. The magnetic spacers 21, 22 are used to provide the downward force F1 to the impeller 26 to balance the upward axial force F4. The magnetic spacers 23, 24 surround a lower portion of the shaft 25 without connection therewith and are positioned below the bearing 27. The magnetic spacers 23, 24 are located so as to be separate and opposite to each other, the magnetic spacer 23 is received in a lower portion of the receiving room of the post 260 and the magnetic spacer 24 is received in the recess 1444 of the shaft support 1440. Each of the magnetic spacers 23, 24 has an N pole and an opposite S pole. The magnetic spacers 23, 24 are arranged so that the S pole of the second magnetic spacer 23 opposes the S pole of the magnetic spacer 24. Since like magnetic poles oppose each other so that a repulsive force F2 exists between the second magnets 23, 24, and the impeller 26 has an upward force F2 exerted on it by the magnetic spacer 21. When the impeller 26 rotates, an axial component force F3 pushes downward on the impeller 26 because of a magnetic interaction between the first permanent magnet 261 and the second magnet 320 of the motor driving unit 30. The magnetic spacers 23, 24 are used to provide the upward force F2 to the impeller 26 to balance the downward axial force F3 and the force G of gravity acting on the impeller 26. When the impeller 26 operates, total axial force acting on the impeller 26 is balanced, wherein the total axial force is illustrated by following equation: F1+G+F3=F2+F4. The four magnetic spacers 21-24 properly suspend the impeller 26 in a stable position in the axial direction such that a bottom of the impeller 26 has no contact with the partition wall 144, whereby a friction between the bottom of the impeller 26 and the partition wall 144 is prevented and noise pollution is considerably reduced. [0018] It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. Continue reading about Miniature pump for liquid cooling system... Full patent description for Miniature pump for liquid cooling system Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Miniature pump for liquid cooling system patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. 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